1. Field of the Invention
The invention relates generally to communication systems, and more particularly to performing an initial ranging function in a communication network.
2. Discussion of Related Art
In today's information age, there is an increasing need for high-speed communication networks that provide Internet access and other on-line services for an ever-increasing number of communications consumers. To that end, communications networks and technologies are evolving to meet current and future demands. Specifically, new networks are being deployed which reach a larger number of end users, and protocols are being developed to utilize the added bandwidth of these networks efficiently.
One technology that has been widely employed and will remain important in the foreseeable future is the shared medium communication network. A shared medium communication network is one in which a single communications channel (the shared channel) is shared by a number of users such that uncoordinated transmissions from different users may interfere with one another. The shared medium communication network typically includes a number of secondary stations that transmit on the shared channel, and a single primary station situated at a common receiving end of the shared channel for receiving the secondary station transmissions. Since communication networks typically have a limited number of communication channels, the shared medium communication network allows many users to gain access to the network over a single communication channel, thereby allowing the remaining communication channels to be used for other purposes.
One type of shared medium communication network divides the shared channel into successive time slots. In such a shared medium communication network, all of the secondary stations must be synchronized with the time slots, so that all secondary station transmissions begin and end within designated time slot(s). Therefore, when a secondary station connects to the shared medium communication network or otherwise attempts to establish a connection in the shared medium communication network, the secondary station performs a ranging function to synchronize with the time slots on the shared channel. The ranging function typically involves an exchange of messages between the primary station and the secondary station by which the secondary station aligns itself with the start of each time slot after compensating for propagation delay and other factors.
One problem in a shared medium communication network involves the ranging of many secondary stations, for example, following a reset or reinitialization of the primary station. For convenience, the ranging of multiple secondary stations following a reset or reinitialization of the primary station is referred to as “initial ranging.” When many secondary stations attempt to perform the ranging function simultaneously, the secondary stations are forced to contend for access to the shared channel. It therefore becomes difficult for any of the secondary stations to complete the ranging function due to the large number of collisions caused by the contention access. As a result, the time needed for all of the secondary stations to complete the ranging function is excessive, and much bandwidth on the shared channel is wasted.
Thus, an efficient initial ranging process is needed.